




public class Main {
    public static void main(String[] args) {
        StringBuffer s = new StringBuffer("哈喽沃德");
        System.out.println(s.charAt(0));
        System.out.println(s.charAt(1));
        System.out.println(s.charAt(2));
        System.out.println(s.charAt(3));
        System.out.println(s);
        System.out.println(s.length());
        s.setCharAt(0, '渣');
        System.out.println(s);
        s.append(s);
        System.out.println(s);
        char[] a = s.toString().toCharArray();
    }
}